Many sources of energy are being wasted. This can be in the form of building air conditioners or refrigeration units that vent heat to the atmosphere, or even the heat given off automobile engines. The U.S. Department of Energy reports that the available seven quadrillion Btu of waste heat sources exceeds the current production of all other U.S. renewable power sources combined. This includes hydroelectric, wood, biofuels, geothermal, wind and solar photovoltaic.

Geothermal power is energy generated by heat stored beneath the Earth's surface. Available in an almost unlimited amount, it currently supplies less than half a percentage point of the world's energy. It is becoming increasingly more accessible and is used widely in the Philippines, Italy, Indonesia, Mexico, New Zealand, Japan, China and Iceland.